[en] Physical and mathematical aspects related to the description of resonant states are presented in a comprehensive way. The concepts concerning the representation of Gamow resonances are revisited in connection with a rigorous mathematical treatment, based on the use of Moeller operators and rigged Hilbert spaces. The formalism is cast in a form amenable for applications to nuclear structure calculations in the continuum

[en] The results of studying the nuclear Hamiltonians in terms of the collective and intrinsic variables are discussed. The BRST-method is adapted to identify the fictions and physical wave functions and operators. The counter terms are added to the Hamiltonian to enforce the break-down of the symmetries, caused by the single-particle field or by the residual two-body interactions. Special attention is paid to the Fermi and Gamow-Teller transitions. The isospin symmetry and calculation of the 0⁺ and 1⁺ states and the Fermi sensitivity and the Gamow-Teller response in the double-beta-decay processes are discussed. The restoration of the Galilean invariance and the nuclear Hamiltonian is studied. The I^π=1^- state is calculated

[en] In this work we discuss possible definitions of the mean value of the energy for a resonant (Gamow) state. The mathematical and physical aspects of the formalism are reviewed. The concept of rigged Hilbert space is used as a supportive tool in dealing with Gamow-resonances

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[en] The single-state-dominance hypothesis (SSDH) states that the decay rates of the two-neutrino double-beta decay are governed by a virtual two-step transition connecting the initial and final ground states through the first 1⁺ state, 1⁺₁, of the intermediate odd-odd nucleus, for those odd-odd nuclei where the 1⁺₁ state is the ground state. To investigate the validity of the SSDH we have performed a systematical theoretical analysis of all known double-beta-decay transitions where the SSDH conditions are fulfilled. The calculations are based on the quasiparticle randon-phase approximation (QRPA) and the results have been obtained by using realistic single-particle bases and realistic interactions. We have studied the double β^- decays of ¹⁰⁰Mo, ¹¹⁰Pd, ¹¹⁴Cd, ¹¹⁶Cd and ¹²⁸Te and the double electron-capture transitions in ¹⁰⁶Cd and ¹³⁶Ce. The analysis shows that the SSDH is realized either through a true dominance of the first intermediate 1⁺ state or by cancellations among the contributions of higher lying 1⁺ states of the intermediate nucleus

[en] The theoretical studies on many-body problems, Hartree-Fock method, nuclear properties and models, and experimental studies in nuclear techniques applied in solid state physics done in La Plata National University, Argentina, by the nuclear physics groups in 1981 and 1982 are reported. (L.C.)

[en] Two-neutrino ββ decay rates of ⁷⁶Ge, ⁸²Se, ^128,130Te are calculated in the quasi-particle random phase approximation using a realistic effective NN interaction. The decays are strongly suppressed, in agreement with the experimental data, when a reasonable amount of particle-particle interaction is taken into account. (orig.)

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[en] In a previous paper we have studied the structure of the Isobaric Analogue State (IAS) using a realistic single-particle model within a formalism that allows to disentangle real effects of isospin violations from spurious effects associated with the construction of basis states. In this work we discuss the influence of the Isovector Monopole State (IMS) on the width of the IAS. According to our results, the presence of a collective IMS is necessary to preserve the empirically found isolation of the IAS from states of the background. This is valid for a simplified harmonic oscillator model and for a realistic single-particle basis as well, since for both cases there is a strong Coulomb mixing between the IAS and the IMS, which increases at the expense of decreasing the mixing between the IAS and the ΔN=0 configuration states. The prediction of the total width of the IAS remains in reasonable agreement with the experimental value in a calculation without free parameters